(i) Field of the Invention
This invention relates to one-piece snap-on, foil-shaped, low drag fairing element for use on long underwater cables.
(ii) Description of the Prior Art
When towing a submerged object, it is usually desirable that induced cable vibrations and noise be suppressed and that cable drag be minimized to achieve maximum depth for a given length of such underwater cable. These objects have been achieved in the past by enclosing the cable with fairings of more or less streamlined shape, or, less effectively with trailing ribbons or hair-like material embedded in the cable.
Cable fairing generally consists of a body attached to the cable to modify the flow characteristics of the water around such cable. In the use of fairing elements in a towed sonar system where a cable is used to tow a submerged body behind a vessel, drag on the towing cable is reduced by fairing elements attached in stacked relation longitudinally along the cable in close abutting relation. It is necessary to wind the tow line, with the fairing attached thereon, onto a winch drum and to accomplish this the fairing must be divided into a number of individual elements. In sonar systems, problems can be encountered from winding the cable with the fairing elements thereon onto the winch drum due to the fact that the fairing elements are rigid which results in a sharp transition in the cable intermediate each adjacent pair of fairing elements. A cable in a sonar system includes a plurality of electrical conductors and sharp bends ultimately can result in breaking one or more conductors. When this happens, the entire cable may have to be replaced.
One such prior art fairing is provided by U.S. Pat. No. 2,397,957 issued Apr. 9, 1946 to H. B. Freeman. That patent alleged to provide a fairing for a cable comprising a plurality of cable-wise normally aligned tail portions, and flexible means covering the tail portions and normally securing them in spaced relation each to the others and forming a head portion for embracing the cable with an easy fit. This was said to permit the fairing, and to a limited extent the separate tail portions, to swivel with respect to the cable.
Another such fairing is provided in U.S. Pat. No. 2,401,783 issued June 11, 1946 to K. H. Wilcoxon. That patent alleged to provide a cable fairing comprising a series of articulated fairing units and spring latch means. This was said to allow for easy releasably securing of the individual units in fairing relation to a cable.
Yet another detachable fairing assembly for use with carriers of sensitive instruments and the like which are towed through a fluid, e.g. water, at some distance from a towing vessel, was said to be provided in U.S. Pat. No. 3,209,718 issued Oct. 5, 1965 to R. L. Rather et al. That patent alleged to provide the combination with a marine towline assembly comprising a load-bearing line and at least one conductor external to such line, the addition of a plurality of removable fairings having two side walls embracing the external conductor at intervals along its longitudinal axis. The fairings were said to include quick-disconnect means for holding the conductor within the side walls of the fairings so as to permit longitudinal movement with respect to the load-bearing line. A plurality of quick-disconnect, snap-on clamps were said to be secured along the load-bearing line, such clamps were said to have at least two arcuate interconnecting pieces for embracing the load-bearing line for transmitting the weight of the fairings and to have holding means to hold the fairings to the load-bearing line.
Still another fairing assembly with convenient snap-on characteristics for a tow-line assembly and which could attempt to overcome the problem that vibrations established on the line often interfered with reliable data results transmitted on the line by setting up false vibration patterns was said to be provided in U.S. Pat. No. 3,241,513 issued Mar. 22, 1966 to R. C. Rather et al. That patent alleged to provide a marine tow-line assembly for use in towing submerged objects. The assembly was said to comprise a channel member, ovoid in cross-section and having bilaterally symmetrical arcuate side walls with the opening through its apex. A line extended through the channel and was laterally removable therefrom. A fin member extended from one of the side walls and in a plane approximately bisecting the apex of the channel member and was said to provide the assembly with hydrodynamic stability. Means were included releasably engaging the line within the apex opening. This was said to retain the line releasably within the channel.
A further such fairing element was provided by Canadian Pat. No. 869,811 issued May 4, 1971 to F. W. W. Pfeiffer, assigned to Fleet Manufacturing Limited. That patent provided a fairing element adapted to be associated with a plurality of such elements in end-to-end abutting relation on a tow line. The fairing element included a rigid body having a pair of opposed longitudinal marginal edges. Means were provided for attaching the tow line or cable to the body to extend along a path intermediate the marginal edges and generally parallel thereto. A pair of opposed ends provided abutting surfaces on the adjacent elements arranged end-to-end and extending along a predetermined path. Means were provided including a portion on one end of the body cooperating with a portion on the opposite end of the body of an adjacent element permitting adjacent elements to remain in contact during angular changes of adjacent elements relative to one another and located such as to minimize any change in pitch length adjacent a path along which the cable is disposed.
Yet another patent proposing an improved fairing element is Canadian Pat. No. 872,007 issued June 1, 1971 to F. W. W. Pfeiffer, assigned to Fleet Manufacturing Limited. That patent provided the fairing elements which had adjacent faces fully in abutting relation when the cable is in a towing condition and a resilient compressible portion on such faces to deform upon the application of higher forces, for example, when the faired cable is wound onto a winch drum. The fairing elements were attached to the cable with the cable spaced inwardly from the marginal edges and thus when the faired cable was wound onto the winch drum, there was a change in curvature of the path followed by the cable. Resilient material was interposed between at least selected portions of adjacent fairing elements allowing compression, i.e., shortening of one edge of the pitch length of fairing element.
Still another such faired cable was provided by Canadian Pat. No. 877,061 issued Aug. 3, 1971 to H. H. Loshigian. That patent provided a faired cable having the outer cross-sectional contours of an airfoil so designed as to have its center of pressure approximately at the quarter chord position (as measured from the leading edge of the section). The forward part of the cross section was constituted by a rearwardly open channel-like or substantially U-shaped relatively less flexible strength member, this shape disposing its shear center considerably forward of its centroid and essentially in the immediate vicinity of the leading edge of the cable section. The aft part of the cross section is attached to the rearwardmost end of the cable part which includes the strength member, e.g., at the ends of the legs of the "U" or flanges of the channel, and has the form of a relatively more flexible tail of substantially triangular shape.
Still another such faired cable was provided in Canadian Pat. No. 887,428 issued Dec. 7, 1971 to H. H. Pearce et al. That patent provided fairings which were interconnected by link means extending between and permitting relative movement of adjacent fairings. Each fairing included a fin member of substantially symmetrical hydrofoil cross section provided with an arcuate opening in the leading edge thereof. The opening was constructed and shaped such that the fairing could be clipped to or unclipped from the tow line. The outer surface of each fairing in the region of the leading edge was provided with guide surfaces converging towards the leading edge.
A still further such faired cable was said to be provided in Canadian Pat. No. 896,987 issued Apr. 4, 1972 to N. E. Hale et al. That patent was alleged to provide a cable fairing for assembly with and in substantial alignment with a plurality of like cable fairings on a cable. The fairing included a flexible hollow nose for accomodating the cable and at least some comparatively rigid tall member, and means for joining the fairing to the next adjacent fairing of a plurality of assembled fairings.
Yet another such faired cable was provided in Canadian Pat. No. 919,998 issued Jan. 30, 1973 to P. B. Kennedy. That patent was said to provide a low-drag, high-speed towing cable for towing submerged objects. The towing cable had an elongated leading edge member and an elongated trailing edge member assembled continuously along a plane parallel to the towing cable elongate dimension to form an overall constant hydrofoil cross-sectional shape.
Still another such faired cable was provided by Canadian Pat. No. 966,015 issued Apr. 15, 1975 to D. Toussainst et al. That patent was said to provide a fairing or jacketing for underwater cables, with streamline profile. The profile was composed of two completely separable profiled strips for individual reeling, each having a first surface to be placed into abutment with the first surface of the respective other first strip and each having a second surface disposed symmetrically to a plane defined by the first surfaces when placed in abutment to each other. The strip each had at least one recess open to the first surface, the recesses having location and contour complementary to each other to define an elongated cavity for loosely receiving the rope or cable when the first surfaces are in mutual abutment. Fastening means were provided on the strips in the first surfaces thereof for releasably interconnecting the two strips between the cavity and the leading edge of the profile, and for releasably interconnecting the two strips between the cavity and the trailing edge of the profile.
Yet another fairing is provided by Canadian Pat. No. 1,018,834 issued Oct. 11, 1977 to J. A. R. Marchag et al.
Still another cable fairing was provided by Canadian Pat. No. 1,045,471 issued Jan. 2, 1979 to T. I. Silvez. This patent provided a hydrodynamic cable fairing section comprising a nose portion, a body portion having two side surfaces and vane means comprising a plurality of vanes connected to each side surface of said body portion. The plurality of vanes was substantially parallel to each other. The nose portion had a continuous curved surface and a longitudinal through bore means for receiving a cable. The body portion extended from the nose portion and tapered from the nose portion towards a trailing edge which forms part of the body portion. Each of the vanes included flat surfaces which tapered toward the trailing edge of the body portion.
Other patents which are of interest in this respect include U.S. Pat. Nos: 3,060,886, 3,092,067, 3,176,646, 3,194,204, 3,233,571, 3,352,274, 3,343,515, 3,343,516 and 3,379,161.